Controlled wetting and spreading of metals on substrates using porous interlayers and related articles

ABSTRACT

The disclosure generally relates to a method of creating patterned metallic circuits (e.g., silver circuits) on a substrate (e.g., a ceramic substrate). A porous metal interlayer (e.g., porous nickel) is applied to the substrate to improve wetting and adhesion of the patterned metal circuit material to the substrate. The substrate is heated to a temperature sufficient to melt the patterned metal circuit material but not the porous metal interlayer. Spreading of molten metal circuit material on the substrate is controlled by the porous metal interlayer, which can itself be patterned, such as having a defined circuit pattern. Thick-film silver or other metal circuits can be custom designed in complicated shapes for high temperature/high power applications. The materials designated for the circuit design allows for a low-cost method of generating silver circuits other metal circuits on a ceramic substrate.

CROSS REFERENCE TO RELATED APPLICATION

Priority is claimed to U.S. Provisional Patent Application 62/658,659,filed Apr. 17, 2018, the entire disclosure of which is incorporatedherein by reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under DE-FE0031250awarded by the U.S. Department of Energy. The government has certainrights in the invention.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The disclosure relates to method for controlled wetting and spreading ofmetals on substrates, in particular where the substrates are difficultto wet with molten metal, such as in the case of ceramic substrates. Themethod includes formation of a porous first metal layer on a substrateto assist wetting of the substrate with a molten second metal, which inturn can form a patterned second metal layer adhered to the substrate.The resulting article including the patterned second metal layer on thesubstrate can be used, for example, in high-temperature and/orhigh-amperage electronic devices.

Background

Ceramic materials are of growing interest to multiple industries fortheir superior mechanical, thermal, and electrical properties. Forexample, ceramic materials are widely used in devices such as solidoxide fuel cells (SOFCs), high-power electronics, cutting tools, andceramic circuit boards. However, practical applications of these ceramicmaterials often requires them to be joined with another material, suchas a metal, to utilize their high thermal conductivity and low thermalexpansion.

High amperage devices require thermally stable materials and uniquecircuit designs to facilitate the demands of current collectors,interconnects, or fuel cells. Often, screen printing is used at anindustrial level to generate printed circuit boards (PCBs) that canaccomplish these tasks. Ceramic PCBs are desired due to their ability tohandle high temperature, high frequency, and high pressure environmentswith great reliability. FIG. 1 illustrates PCBs on a ceramic substrate(left) and a conventional substrate (right).

Ceramic substrates such as alumina, aluminum nitride, or beryllium oxideare highly thermally conductive and can dissipate heat quickly across asurface, preventing heat build-up and improving the life ofsemiconductor junctions on the PCB. Therefore, ceramic substrates areideal for high amperage and high temperature devices. Nickel is oftenused in industry as a connector for the screen printing process andbridges the gap between circuit material and ceramic substrate.

Many large scale producers of PCBs utilize circuit paste as a materialto connect surface-mounted components to pads on the board. Circuitpaste is distributed in a sticky-viscous form and is solidified underlarge amounts of heat to generate a mechanical connection. However,methods of application for circuit paste often introduce defects in theconnection. Defects such as too much solder, or solder bridging canoccur, and such defects can be exasperated by high-temperatureenvironments.

Reactive wetting is a method for improving wetting of metals on ceramicsubstrates. In reactive wetting, the addition of reactive elements suchas Si, Ti, Zr, and Ge are introduced to the liquid metal to assist inthe dissolution of the ceramic substrate and/or formation of newreaction compound(s) at the ceramic/liquid metal interface. However,this process generally requires a protective atmosphere, and mostcommonly high vacuum, for the chemical stability of these added reactiveelements, making this method costlier and not viable for industrialapplications. An alternative route for reactive wetting is to achieve areactive surface layer on the ceramic substrate rather thanincorporating reactive elements into the liquid metal. This process,however, is usually performed using a number of surface coating stepsand thus has higher costs.

Therefore an alternative for ceramic substrate PCBs is needed.

SUM MARY

In one aspect, the disclosure relates to a method for forming apatterned metal layer on a substrate, the method comprising: (a)providing a porous wetting substrate comprising: (i) an underlyingsubstrate, and (ii) a porous first metal layer on a surface of theunderlying substrate; (b) applying (or contacting) a patterned secondmetal material to the porous wetting substrate and in contact with theporous first metal layer thereon, the second metal having a lowermelting point than that of the first metal; and (c) heating the secondmetal (e.g., in a protective or inert atmosphere) at a temperature andpressure sufficient to melt the second metal material, wet pores of theporous first metal layer with the molten second metal material, andcontact the underlying substrate with the molten second metal material,thereby forming a wetted substrate comprising the underlying substrate,and a patterned, wetted second metal layer adhered to the underlyingsubstrate (e.g., via the porous first metal layer). In part (a), theporous first metal layer is suitably adhered to the underlyingsubstrate, such as resulting from a pre-sintering process or otherwise.Suitably, the second metal melting point is at least 25, 50, 100, 200,or 300° C. and/or up to 300, 500, 700 or 1000° C. lower than the firstmetal melting point. Similarly, the second metal melting point issuitably lower than the melting or thermal decomposition points of theunderlying substrate. In part (c), the heating temperature is suitablysufficiently high to melt the second metal material, but far enoughbelow the melting point of the first metal such that the porous firstmetal layer does not melt or otherwise disintegrate before its porousstructure promotes the wetting and contact of the substrate with themolten second metal material. The final, solid patterned second metallayer forms after cooling of the wetted substrate (e.g., with the secondmetal material still in liquid form), for example returning to ambienttemperature and pressure conditions without elevated heatingtemperatures and/or an inert protective atmosphere. The patterned secondmetal layer generally can include at least one or two portions: a bulksecond metal layer and optionally an interfacial layer between the bulksecond metal layer and the substrate.

In another aspect, the disclosure relates to a method for forming anelectronic apparatus or component, the method comprising: (a) performingthe above method in and of its variously disclosed embodiments to formthe wetted substrate comprising the underlying substrate, and apatterned, wetted second metal layer adhered to the underlyingsubstrate, wherein the patterned second metal material has a spatialpattern corresponding to electronic circuitry; and (b) mounting one ormore electronic components (e.g., processor, memory) to the wettedsubstrate in electrical connection to an element of the patterned,wetted second metal layer. The electronic components also can beinterconnected with each other via one or more second metal patternelements. The electronic components and/or integrated electronic systemssuitable for manufacture and use as a high-temperature PCB are notparticularly limited. Examples include industries that needhigher-frequency connections and good heat resistance that can benefitfrom ceramic PCBs, for example including automotive components,aerospace components, medical device components, heavy machinerycomponents, monitors for drilling equipment and related components,sensors in heat engines of any kind, RF resistors and terminations ,andLED chips.

In another aspect, the disclosure relates to a patterned, wettedsubstrate: (a) a substrate; (b) a bulk patterned second metal layeradjacent to the substrate, the bulk second metal layer comprising asecond metal and optionally a first metal, the first metal being at alower concentration than the second metal in the bulk patterned secondmetal layer when present; and (c) an interfacial layer between the bulkpatterned second metal layer and the substrate, the interfacial layercomprising the first metal; wherein the second metal has a lower meltingpoint than that of the first metal. The bulk patterned second metallayer (e.g., as an outer, top, or external layer) generally includesonly minor amounts of the first metal (e.g., up to 1, 2, 5 wt. % of aminor immiscible component in a primary component). A large portion ofthe first metal can remain as an interfacial layer on the substrate,positioned between the substrate and the bulk second metal layer. Theinterfacial layer can include portions of the porous first metal layerremaining at least partially or substantially intact as a discretestructure of the interfacial layer in which the pores have been wettedor infiltrated by the second metal material. The interfacial layer canhave the same pattern corresponding to that of the bulk patterned secondmetal layer (e.g., as a result of an initially patterned first porousmetal layer).

Various refinements of the disclosed patterning methods, methods forforming an electronic component, and patterned, wetted substrate arepossible.

In a refinement, the porous first metal layer has a spatial patterncorresponding (or complementary) to that of the patterned second metalmaterial. The porous first metal layer can be formed in the same(two-dimensional) spatial pattern as the second metal material generallyusing the same techniques described below for forming the patternedsecond metal material, for example by printing or otherwise applying afirst metal mixture including a first liquid formulation and first metalparticles in a predetermined pattern on the substrate, followed bypre-sintering. In some embodiments, the second metal layer is applied inthe desired pattern on the complementary pattern of the porous firstmetal layer. In other embodiments, for example when the first porouslayer has a continuous and interconnected patterned structure, thesecond metal layer can be applied over the first porous layer in anydesired pattern or with no pattern (e.g., as a continuous overlayer ofsecond metal material). In such cases, upon melting of the second metal,the molten second metal will then be wicked to infiltrate or fill thefirst porous metal layer patterned network and become a dense structurewith the same design or pattern of the first porous metal layer (e.g.,due to the relative lack of adhesion between the second metal materialand substrate). For example, if the lower melting point second metal isin contact with the first porous metal (e.g., adjacent, beside, etc. thefirst porous metal layer), the second metal could be patterned asadjacent reservoirs and be printed on the same substrate surface as thehigher melting point material, and the second metal would besubsequently wicked into the desired pattern of the first porous metallayer upon melting. In another embodiment, the lower melting pointsecond metal layer can be deposited on the substrate and below the firstporous metal layer (e.g., by methods such as sputtering). In such cases,the deposition of the first porous metal layer (e.g., in the desiredpattern for the second metal layer) can wet the sputtered second metallayer and bring the first porous metal layer into contact with thesubstrate, thus bonding the second metal layer to the substrate in thedesired pattern. The molten second metal material not close to the firstporous metal layer will be wicked away from the interface by the surfacetension with the first porous metal layer.

In a refinement, the patterned second metal material has a spatialpattern corresponding to electronic circuitry (e.g., electrodes, wires,interconnects). For electronic circuitry applications, the patternedsecond metal material suitably includes a metal with high electricalconductivity, such as silver or copper. The minimum dimension (e.g.,line width) of the patterned second metal material can be controlled,for example, based on the powder size of the initial second metalmaterial (e.g., when deposited as a suspension in a liquid formulationprior to melting) and/or the deposition technique (e.g., screenprinting,3D printing etc.). For example, with the screenprinting used in theillustrative embodiments in the example, lines with a width as low asabout 200 μm can be produced. In other embodiments, minimum pattern linewidths of about 50, 80, 100, 120, or 150 μm can be used, for exampleminimum pattern line widths of at least 50, 80, 100, 120, 150, or 200 μmand/or up to 100, 150, 200, 500, or 1000 μm.

The spatial patterns, whether for electronic circuitry or otherwise, canbe formed by lithographic methods, for example where there is a maskthat is preferentially removed to deposit a desired material, such as byelectro deposition. Lithographic methods could be used to providemasking of regions where the first porous metal layer would not beapplied to the substrate, enabling other methods of applying a porousmetal powder onto the exposed substrate, by means of liquid or gasassisted electrostatic methods for particle deposition, on which auniform deposition of the lower melting point second metal materialcould be deposited by various methods, such as sputtering,electrodeposition, etc. Also, additive manufacturing methods could beused to deposit first metal powder particles and concurrently locallyheat the deposited powder to partially sinter particles to adhere to thesubstrate, for example in the desired pattern. More generally, thehigher melting temperature porous first metal layer serves to alter theinterfacial energies between the three components (i.e., first andsecond metals, substrate), thus promoting wetting between the lowermelting temperature second metal layer and the substrate. Any spatialarrangement of the three components can be used, as long as it promotesbonding or adhesion between the lower melting temperature second metaland the substrate (e.g., ceramic or otherwise).

In a refinement, the first metal comprises at least one of nickel,aluminum, cobalt, iron, copper, titanium and combinations thereof (e.g.,mixtures or alloys thereof); and the second metal comprises at least oneof silver, aluminum, tin, bismuth, nickel, copper, gold, cobalt, andcombinations thereof (e.g., mixtures or alloys thereof). Some metalssuch as aluminum, nickel, cobalt, copper could be useful as either thefirst or second metal based on its particular melting point relative tothe other metal. Examples of specific combinations of first/secondmetals include Ni/Ag, Fe/Ag, Co/Ag, Al/Sn, Cu/Bi, and Fe/Bi. The firstmetal or alloy is preferably selected for its relative slowness tooxidize, such as Ni, Co, Fe, and Co—Ni (alloy), which have some degreeof oxidation resistance and a high relative melting point compared to asecond metal selection. In some cases, the first/second metalcombinations are selected such that the first and second metals arerelatively immiscible in each other such that a bulk layer in the finalstructure is substantially composed of a bulk second metal layer (e.g.,as an outer, top, or external layer) with only minor amounts of thefirst metal (e.g., up to 1, 2, 5 wt. % of a minor immiscible componentin a primary component). A large portion of the first metal can remainas an interfacial layer on the underlying substrate, or positionedbetween the substrate and the bulk second metal layer. The interfaciallayer can include portions of the porous first metal layer remaining atleast partially or substantially intact as a discrete structure of theinterfacial layer in which the pores have been wetted or infiltrated bythe second metal material. In yet other cases the first metal could bemiscible with the second metal and dissolve into the bulk second metallayer as a homogeneous component (e.g., up to 1, 2, 5, 10, 20, or 30 wt.% of a minor miscible component in a primary component). Preferably, thefirst metal, the second metal, and the substrate are selected based on arelative inability of the second metal to wet the substrate material inisolation, for example being characterized by wetting/contact angles ofthe second metal on the first metal or the substrate materialindividually of at least 20°, 30°, 40°, or 50° when measured in air oran inert atmosphere such as nitrogen. The porous nature of the firstmetal layer promotes efficient wetting by the molten second metal ofboth the porous first metal layer and the first substrate.

In a refinement, the underlying substrate comprises a ceramic material(e.g., generally an inorganic, non-metallic oxide, nitride or carbidematerial).

In a further refinement, the ceramic material is selected from the groupconsisting of aluminum oxide, aluminum nitride, gallium nitride,aluminum gallium nitride, aluminum gallium indium nitride, berylliumoxide, zirconium oxide, cerium oxide, zinc oxide, silicon carbide,silicon nitride, tungsten carbide, doped derivatives thereof, andcombinations thereof. A doped derivative can include any of theforegoing ceramic material, for example with up to about 5, 10, or 15mol. % of other elements or oxides added thereto.

In a further refinement, the ceramic material comprises one or more ofaluminum oxide (alumina), aluminum nitride, gallium nitride, aluminumgallium nitride, aluminum gallium indium nitride, beryllium oxide,silicon carbide, and silicon nitride. Alumina, aluminum nitride,beryllium oxide, and silicon nitride are particularly suitable forcircuit board materials, given their favorable thermal conductivity andability to withstand and dissipate heat. Alumina with different puritiescan be used as well as alumina with different dopants too (e.g., Zr).Alumina is a suitable substrate for near-room-temperature electronics.Ceramics such as gallium nitride, aluminum gallium indium nitride, andsilicon carbide are particularly suitable for electronics operating hightemperatures, such as 250° C. to 900° C., especially high powerelectronics.

In a further refinement, the ceramic material comprises a stabilizedzirconium oxide (zirconia) (e.g., a ceramic in which the crystalstructure of zirconium dioxide is stabilized at room temperature by anaddition of an additional oxide material such as up to about 10 mol. %of the additional oxide). For example, the stabilized zirconium oxide(zirconia) can be selected from the group consisting of yttrium oxide(yttria)-stabilized zirconia (YSZ), calcium oxide (calcia)-stabilizedzirconia, magnesium oxide (magnesia)-stabilize zirconia, cerium oxide(ceria)-stabilized zirconia, scandium oxide (scandia)-stabilizedzirconia, aluminum oxide (alumina)-stabilized zirconia, cerium oxide,doped cerium oxide, and combinations thereof (e.g., common SOFC solidelectrolytes include yttria-stabilized zirconia (YSZ) such as with 8mol. % yttira, scandia-stabilized zirconia (ScSZ) such as with 9 mol. %scandia, and gadolinium doped ceria (GDC)).

In a further refinement, the ceramic material comprises one or more oflanthanum strontrium manganite, lanthanum strontium cobaltite, andlanthanum strontium ferrite. Such ceramic materials can be useful insolid oxide fuel cell (SOFC) electrodes.

In a refinement, the underlying substrate comprises one or more of ametal material and a semiconductor material. A metallic substrate can beuseful if the second metal (e.g., silver or otherwise) does not havevery good wetting properties on the metallic substrate. In anembodiment, a metallic substrate can include a ceramic coating on thesurface (e.g., a stainless steel with alumina coating), and the firstand second metals according to the disclosure can be applied to theceramic coating of the substrate.

In a refinement, the porous first metal layer has a thickness rangingfrom 0.01 μm to 250 μm, such as 5 μm to 40 μm or 10 μm to 30 μm (e.g.,at least 0.01, 0.1, 1, 2, 3, 5, 8, 10, 15, 20, or 30 μm and/or up to 10,20, 30, 40, 60, 100, 200, or 250 μm). The porous first metal layer neednot have a uniform thickness, and the foregoing thickness values canrepresent an average layer thickness and/or a range for a spatiallyvariable local layer thickness.

In a refinement, the porous first metal layer comprises pores ranging insize from 0.005 μm to 50 μm (e.g., at least 0.005, 0.05, 0.5, 1, 2, 3,5, or 10 μm and/or up to 5, 10, 15, 20, 30, or 50 μm). The foregoingsize values can represent an average pore size and/or a range fordistributed pores sizes throughout the first metal layer.

In a refinement, providing the porous wetting substrate comprises: (a1)applying to the underlying substrate a layer of a first metal mixturecomprising a first liquid formulation and first metal particlesdispersed in the first liquid formulation; and (a2) (optionally)pre-sintering the layer of the first metal mixture (e.g., in aprotective pre-sintering atmosphere) at a temperature and pressuresufficient to remove the first liquid formulation and at least partiallysinter the first metal particles, thereby forming the porous first metallayer (e.g., adhered to the underlying substrate). The first metalmixture suitably is in the form of a solution, thick paste, orsuspension, etc. that coats the first substrate in the target area ofinterest. The first metal mixture can include at least 30, 50, or 70 wt.% first metal particles and/or up to 50, 70, or 90 wt. % first metalparticles, at least 10, 30, or 50 wt. % liquid formulation and/or up to30, 50, or 70 wt. % liquid formulation. The liquid formulation caninclude a liquid solvent medium (e.g., water, isopropanol or otheralcohol or organic solvent), a liquid binder to improve green strength(e.g., a polymeric binder dissolved in the solvent medium), and/or adispersant to prevent agglomeration of the first metal particles in astable first metal mixture (e.g., a polymeric dispersant dissolved inthe solvent medium). Pre-sintering generally includes subjecting thefirst metal mixture layer to a gradually ramping temperature thatremoves the liquid formulation, for example degrading, decomposing, etc.any polymer additives therein and at least partially fusing the firstmetal particles to form the porous first metal layer. Sinteringgenerally includes applying heat and/or pressure at a level and timesufficient to fuse the particles of the sintering composition withoutsubstantial melting such as to liquefaction. In some alternativeembodiments, the porous first metal layer can be applied not onlythrough deposition techniques, but also by other chemical approaches,for example by coating the substrate surface with a metal oxide layer(e.g., NiO) which is then reduced to a corresponding metal (e.g., Ni)and also generates nano- or meso-scale porosity in the metal during thereduction process. In some alternative embodiments, a separatepre-sintering step (a2) before heating the second metal can be omitted,for example when the heating of the second metal is sufficient to inducesintering of the first metal mixture layer and form the porous firstmetal layer prior to and/or concurrently with the molten second metal.

In a further refinement, the first liquid formulation comprises apolymeric solution. The liquid formulation can generally include anypolymeric binder, dispersant, resin, or other liquid vehicle. In somecases, the polymeric binder can be a curable binder such that thecorresponding cured binder or resin is degradable at an intermediatetemperature between its curing temperature and the pre-sinteringtemperature. An example binder system includes ethylene glycol monobutylether, ethylene glycol, and isopropanol.

In a further refinement, the first metal mixture layer has a thicknessranging from 0.01 μm or 2 μm to 100 μm, such as 5 μm to 40 μm or 10 μmto 30 μm (e.g., at least 0.01, 0.1, 1, 2, 3, 5, 8, 10, or 15 μm and/orup to 10, 20, 30, 40, 60 or 100 μm). The foregoing thickness values canrepresent an average layer thickness. The first metal mixture layer canbe comparable but generally larger in thickness relative to that of theeventual porous first metal layer.

In a further refinement, the first metal particles have a size rangingfrom 0.01 μm or 2 μm to 50 μm (e.g., a number-, mass-, or volume-averageparticle size or diameter, such as at least at least 0.01, 0.1, 1, 2, 3,5, 8, or 10 μm and/or up to 10, 20, 30, 40, 50 μm; such as 3 μm to 20 μmor 5 μm to 10 μm). The foregoing ranges can similarly represent the span(such as D10-D90) of the first metal particle size distribution. In ayet further refinement, the porous first metal layer has a thicknessranging from 1 to 10 (e.g., 1.5 or 2 to 5 or 8) times the averageparticle size of the first metal particles prior to pre-sintering (e.g.,relative to the number-, mass-, or volume-average particle size ordiameter of the first metal particles as added to the first metalmixture).

In a further refinement, pre-sintering comprises heating the layer ofthe first metal mixture to a maximum temperature ranging from 600° C. to1400° C. (e.g., at least 600° C., 800° C., or 1000° C. and/or up to1000° C., 1200° C., or 1400° C.). Alternatively or additionally,pre-sintering heating can comprise heating to a maximum temperature thatis at least 100, 200, or 300° C. and/or up to 300, 500, or 700° C. lowerthan the first metal melting point, such as ramping from ambient/roomtemperature of first metal mixture application at a rate of about 2-10,50, or 100° C./minute up to the maximum temperature, optionally holdingat the maximum temperature for up to 0.1-5 hours, and then reducing thetemperature back to ambient/room temperature at a rate of about 2-10,50, or 100° C./minute. Pre-sintering is performed at a temperaturesufficient to eliminate the liquid formulation (e.g., evaporate solvent,decompose/eliminate any polymeric additives), but less than atemperature sufficient to fully sinter the first metal. At suchtemperatures, partial sintering/fusing of some particles can occur to adegree sufficient to provide a porous first metal structure even in theabsence of polymeric additives.

In a further refinement, the method comprises performing pre-sinteringin a protective pre-sintering atmosphere comprising at least one ofargon and nitrogen (e.g., more generally any inert or protectiveatmosphere that avoids or prevents oxidation of the first metalparticles during pre-sintering). The protective pre-sintering atmospherecan be essentially completely inert gases such as argon, nitrogen, or amixture thereof, such as at least 90, 95, 98, 99, or 99.9 mol. % inertgases. A reducing gas such as hydrogen can be included in the protectiveatmosphere to protect against oxidation, such as at least 1 or 2 mol. %and/or up to 5 or 10 mol. % reducing gas. The protective atmosphere isgenerally at a pressure of about 1 atm or slightly higher to limit entryof external air during pre-sintering. The partial pressure of oxygen gas(pO₂) in the protective atmosphere is generally selected to maintain ametallic surface on the first metal particles and porous layer, whichcan vary with the particular type of first metal, but is suitably about10⁻⁶ atm or less in many cases.

In a refinement, applying a patterned second metal material comprises:(b1) applying to the porous wetting substrate a patterned layer of asecond metal mixture comprising a second liquid formulation and secondmetal particles dispersed in the second liquid formulation. The secondmetal mixture suitably is in the form of a solution, thick paste, orsuspension, etc. that coats the porous wetting substrate (e.g., onto theporous first metal layer thereof) in the target area of interest. Thesecond metal mixture is applied in a pattern on the porous wettingsubstrate, for example via a printing process (e.g., application of aliquid or semi-liquid second metal mixture with a print head in fluidcommunication with a reservoir of the second metal mixture) in apreselected, controlled pattern. Other methods of applying a patternedsecond metal material (e.g., using a second metal mixture including thesecond liquid formulation or otherwise) can include tape-casting,deposition, masking coating, and 3D printing. The second metal mixturecan include at least 30, 50, or 70 wt. % second metal particles and/orup to 50, 70, or 90 wt. % second metal particles, at least 10, 30, or 50wt. % liquid formulation and/or up to 30, 50, or 70 wt. % liquidformulation. The second liquid formulation can include a liquid solventmedium (e.g., water, isopropanol or other alcohol or organic solvent), aliquid binder to improve green strength (e.g., a polymeric binderdissolved in the solvent medium), and/or a dispersant to preventagglomeration of the second metal particles in a stable second metalmixture (e.g., a polymeric dispersant dissolved in the solvent medium).

In a further refinement, the second liquid formulation comprises apolymeric solution. The second liquid formulation can generally includeany polymeric binder, dispersant, resin, or other liquid vehicle. Insome cases, the polymeric binder can be a curable binder such that thecorresponding cured binder or resin is degradable at an intermediatetemperature between its curing temperature and the heating/meltingtemperature of the second metal material. An example binder systemincludes ethylene glycol monobutyl ether, ethylene glycol, andisopropanol.

In a further refinement, the second metal mixture layer has a thicknessranging from 0.01 μm or 2 μm to 500 μm, such as 5 μm to 40 μm or 10 μmto 30 μm (e.g., at least 0.01, 0.1, 1, 2, 3, 5, 8, 10, or 15 μm and/orup to 10, 20, 30, 40, 60, 100, 150, 200, or 500 μm). The foregoingthickness values can represent an average layer thickness. The secondmetal mixture layer can be comparable but generally larger in thicknessrelative to that of the eventual patterned, wetted second metal layer.

In a further refinement, the second metal particles have a size rangingfrom 0.01 μm or 2 μm to 50 μm (e.g., a number-, mass-, or volume-averageparticle size or diameter, such as at least at least 0.01, 0.1, 1, 2, 3,5, 8, or 10 μm and/or up to 10, 20, 30, 40, 50 μm; such as 3 μm to 20 μmor 5 μm to 10 μm). The foregoing ranges can similarly represent the span(such as D10-D90) of the second metal particle size distribution. In ayet further refinement, the second metal mixture layer has a thicknessranging from 1 to 10 (e.g., 1.5 or 2 to 5 or 8) times the averageparticle size of the second metal particles prior to heating (e.g.,relative to the number-, mass-, or volume-average particle size ordiameter of the second metal particles as added to the second metalmixture).

In a refinement, applying a patterned second metal material comprises:(a1) applying to the underlying substrate a patterned layer of a firstmetal mixture comprising a first liquid formulation and first metalparticles dispersed in the first liquid formulation; (a2) pre-sinteringthe patterned layer of the first metal mixture at a temperature andpressure sufficient to remove the first liquid formulation and at leastpartially sinter the first metal particles, thereby forming a patternedporous first metal layer; (b1) applying the second metal material to theporous wetting substrate and in contact with the patterned porous firstmetal layer thereon; and (c1) heating the second metal at a temperatureand pressure sufficient to melt the second metal material, wet pores ofthe patterned porous first metal layer with the molten second metalmaterial, and contact the underlying substrate with the molten secondmetal material, thereby forming a wetted substrate comprising theunderlying substrate, and a patterned, wetted second metal layer adheredto the underlying substrate with a pattern corresponding to that of thepatterned porous first metal layer.

In a refinement, heating the second metal comprises: (c1) heating thesecond metal to a maximum temperature ranging from 600° C. to 1200° C.(e.g., at least 600° C., 800° C., or 1000° C. and/or up to 1000° C.,1100° C., or 1200° C.). Alternatively or additionally heating cancomprise heating to a maximum temperature above the second metal meltingpoint of the second metal but less than the first metal melting point,such as at least 25, 50, 100, 200, or 300° C. and/or up to 300, 500, or700° C. lower than the first metal melting point; such as ramping fromambient/room temperature at a rate of about 2-10, 50, or 100° C./minuteup to the maximum temperature, optionally holding at the maximumtemperature for up to 0.1-5 hours, and then reducing the temperatureback to ambient/room temperature at a rate of about 2-10, 50, or 100°C./minute. The heating process is performed at a temperature andpressure sufficient to melt the second metal material. The molten secondmetal material then wets the pores of the porous first metal layer topenetrate the first metal layer pores and contact the underlyingsubstrate with controlled/limited (lateral) spreading such that themolten second metal material retains substantially the same(two-dimensional) spatial pattern of the patterned second metal materialas applied to the porous wetting substrate. The result of the heatingprocess is a wetted substrate including the substrate and a patterned,wetted second metal layer adhered to the substrate. Heating generallyincludes subjecting the second metal to a gradually ramping temperaturethat removes the second liquid formulation (when present and used toapply a second metal mixture including the second metal as describedabove), for example degrading, decomposing, etc. any polymer additivestherein and melting the second metal particles to form the molten secondmetal and patterned, wetted second metal layer.

In a refinement, the method comprises performing heating the secondmetal in a protective atmosphere comprising at least one of argon andnitrogen (e.g., more generally any inert or protective atmosphere thatavoids or prevents oxidation of the nickel porous layer during heating).The protective heating atmosphere can be essentially completely inertgases such as argon, nitrogen, or a mixture thereof, such as at least90, 95, 98, 99, or 99.9 mol. % inert gases. A reducing gas such ashydrogen can be included in the protective atmosphere to protect againstoxidation, such as at least 1 or 2 mol. % and/or up to 5 or 10 mol. %reducing gas. The protective atmosphere is generally at a pressure ofabout 1 atm or slightly higher to limit entry of external air duringheating. The partial pressure of oxygen gas (pO₂) in the protectiveatmosphere is generally selected to maintain a metallic surface on thefirst and second metals, which can vary with the particular type offirst and second metals, but is suitably about 10⁻⁶ atm or less in manycases.

In a refinement, the second metal material comprises at least 90 wt. %of the second metal (e.g., at least 90, 95, 98, 99, or 99.9 wt. % secondmetal, with the balance being other alloy or impurity elements).

In a refinement, the second metal material is free from air-reactivecomponents. For example, the second metal material can be free fromoxygen-reactive components such as reducible or oxidazable species, suchas copper, indium, zirconium, titanium, zinc, tin, manganese, lithium,and/or silicon, and further including species containing the foregoingelements (e.g., copper-containing species such as CuO).

In a refinement, the patterned, wetted substrate further comprising oneor more electronic components (e.g., processor, memory) mounted to theto the pattern, wetted substrate in electrical connection to an elementof the bulk patterned second metal layer; wherein the bulk patternedsecond metal layer has a spatial pattern corresponding to electroniccircuitry. The electronic components also can be interconnected witheach other via one or more second metal pattern elements.

In a refinement of the patterned, wetted substrate, the bulk patternedsecond metal layer has a first metal concentration of 20 wt. % or less(e.g., comprising at least 0.1, 1, 2, or 5 wt. % and/or up to 1, 2, 5,10, 15, or 20 wt. % first metal, where the concentration can representan average concentration across the bulk second metal layer and/or arange spanning/including the local maximum and minimum concentrationacross the bulk second metal layer); and the interfacial layer has afirst metal concentration of at least 10 wt. % and greater than thefirst metal concentration of the bulk patterned second metal layer(e.g., at least 10, 15, 20, or 30 wt. % and/or up to 30, 40, 50, 60, 80,90, or 95 wt. % first metal, where the concentration can represent anaverage concentration across the interfacial layer and/or a rangespanning/including the local maximum and minimum concentration acrossthe diffusion layer). Relative high/low concentrations of the firstmetal in the interfacial layer and the bulk patterned second metal layercan be based on the average first metal values in the correspondinglayers.

In a refinement of the patterned, wetted substrate, the bulk patternedsecond metal layer has a second metal concentration ranging from 70 wt.% to 99 wt. % (e.g., at least 70, 80, 90, or 95 wt. % and/or up to 75,85, 95, 98, or 99 wt. % second metal). The concentration can representan average concentration across the bulk patterned second metal layerand/or a range spanning/including the local maximum and minimumconcentration across the bulk patterned second metal layer.

In a refinement of the patterned, wetted substrate, the bulk patternedsecond metal layer is substantially free from discrete first metalparticles having a size greater than 1 μm. For example the originalporous first metal layer formed during fabrication can be essentiallycompletely disintegrated. The first metal present in the bulk secondmetal layer can be in the form of a continuous mixture or alloy with thesecond metal and not as discrete larger first metal particles such asthose originally used to form the porous first metal layer.Alternatively or additionally, first metal present in the bulk secondmetal layer can be present in sub-micron sized discrete particles fromthe porous first metal layer that were not completely disintegratedduring heating, such as less than 1000, 500, 200, 100, or 10 nm in sizewhether on average or for the entire distribution.

While the disclosed compounds, articles, methods and compositions aresusceptible of embodiments in various forms, specific embodiments of thedisclosure are illustrated (and will hereafter be described) with theunderstanding that the disclosure is intended to be illustrative, and isnot intended to limit the claims to the specific embodiments describedand illustrated herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and accompanying drawingswherein:

FIG. 1 illustrates printed circuit boards (about 8 cm×5 cm) on a ceramicsubstrate (left) and a conventional substrate (right).

FIG. 2 illustrates silver circuits formed on ceramic (alumina)substrates using a porous nickel interlayer according the disclosure(scale bar=1 mm).

FIG. 3 provides a cross sectional view of the silver/nickel/ceramiccircuit embodiment of FIG. 2, with some degree of oxidation beingevident in the right panel (scale bar=100 μm in both panels).

FIG. 4 is a schematic illustrating the method according to thedisclosure.

FIG. 5 includes top view images (top row) and side cross sectionalimages (bottom row) of patterned silver circuit structures on an aluminasubstrate with a porous nickel interlayer (scale bar=1 mm for top row,100 μm for bottom row).

FIG. 6 illustrates an embodiment of the disclosed method in which thesecond metal layer is formed into the desired pattern byself-infiltration into a porous first metal layer having the desiredpattern (scale bar=5 mm for top three rows, 100 μm for bottom row).

FIG. 7 illustrates two applications of the methods of the disclosure (Aand B) that can be employed to achieve patterned metallic circuits.

DETAILED DESCRIPTION

The disclosure generally relates to a method of creating patternedmetallic circuits (e.g., silver circuits) on a substrate (e.g., aceramic substrate). In this process, a porous metal interlayer (e.g.,porous nickel) is applied to the substrate to improve wetting andadhesion of the patterned metal circuit material to the substrate. Thesubstrate is heated to a temperature sufficient to melt the patternedmetal circuit material but not the porous metal interlayer. Spreading ofmolten metal circuit material on the substrate is controlled by theporous metal interlayer, which can itself be patterned, such as having adefined circuit pattern. Thick-film silver or other metal circuits canbe custom designed in complicated shapes for high temperature/high powerapplications. The materials designated for the circuit design allows fora low-cost method of generating silver circuits other metal circuits ona ceramic substrate. FIG. 2 illustrates silver circuits formed onceramic (alumina) substrates using a porous nickel interlayer having acomplementary pattern to that of the silver circuits and three differentrepresentative length/size scales.

Common manufacturing processes use physical vapor deposition (PVD) toproduce silver circuits. The PVD process is expensive and generatesporous and thin circuits creating large amounts of resistance. The highresistance consequence of PVD is not ideal for high amperageelectronics. The disclosed method advantageously generates dense silvercircuits with tunable thickness ranging from 10 microns to 1 millimeter,thereby making the method and resulting articles suitable forhigh-temperature, high-amperage applications. Another potentialapplication for the technology is the ability to use the silver as a wayto bond ceramics together.

Oxidation testing of the resulting articles has been conducted withimages of the results displayed below in FIG. 3 forsilver/nickel/ceramic embodiment illustrated in FIG. 2. As seen in theright panel of FIG. 3, some oxidation of the nickel does occur, with thedarker grey region in right panel corresponding to NiO, the lighter greyregion corresponding to Ni, the white region corresponding to Ag, andthe dark bottom portion is the ceramic substrate. Oxidation is harmfulto the circuit components, because it weakens the connection of thesilver to the ceramic substrate. However, the mechanical durability ofthe circuit was unaffected by the small amounts of oxidation present inthe fabricated examples.

In a particular embodiment of the disclosure, a porous interlayer ofnickel on a ceramic substrate can be used to control the wetting andspreading of molten silver on the ceramic substrate, which is otherwisedifficult to wet directly with silver. This technique can be used toproduce silver circuits on ceramic substrates. As shown in FIG. 2, themethod can be used to produce inexpensive thick-film silver circuits incomplicated shapes for high-temperature/high-power applications using aporous interlayer of nickel (which can also be patterned) on a ceramicsubstrate. Unlike existing physical vapor deposition (PVD) processeswhich produce dense silver circuits but are expensive and limited tothin circuit lines (e.g., 1 micron or less thick) that cannot handlehigh power, or existing thick-film techniques which produce thick (e.g.,up to 100 microns thick) silver circuits that are porous and hence havean undesirably higher resistance, the silver circuits according to thedisclosure (e.g., a patterned silver circuit on a porous nickelinterlayer) are both dense and thick. The high density/lack of porosityand high thickness of patterned metal layers (e.g., formed from silveror otherwise) formed according to the disclosure results in a lowresistivity of the patterned metal layers suitable for high powerapplications. The patterned metal layers also can be fabricated madeinexpensively (e.g., via screen printing). The patterned metal layerssuitably can have a controlled thickness, for example ranging from about10 μm to about 1 mm (e.g., at least 10, 20, 50, or 100 μm and/or up to50, 100, 200, 500, or 1000 μm).

FIG. 4 schematically illustrates the method according to the disclosure,which improves the wetting and controls the spreading of liquid silveror other metal on ceramic or other substrates. As illustrated in FIG. 4for the specific case of silver adhered to a ceramic substrate using aporous nickel interlayer, the ternary presence of nickel alters thesurface energy between the ceramic and liquid silver so that spontaneousinfiltration occurs with wetting angles between silver and the ceramicbeing significantly lower than between the binary ceramic and liquidsilver system. The heating, wetting, and spreading is suitably performedin an inert atmosphere.

FIG. 5 illustrates the disclosed method as applied to form a patternedsilver layer on a ceramic substrate, for example as an illustrativeelectric circuit design for high power/temperature electronics that useceramic boards. Three layers of nickel paste and then six layers ofsilver paste were printed in the illustrated circuit pattern onto analumina substrate in a (decorative) circuit pattern. In otherapplications, the nickel particles/porous layer and silver could beapplied by various techniques like tape-casting, deposition, maskingcoating, 3D printing etc. Alternatively, any other method of achieving aporous nickel layer on a ceramic substrate could be used (e.g., airbrushing, electroless coating, etc.). Then the assembly was heated up toabout 1000° C. to melt only the silver in argon (inert atmosphere),allowing the molten silver to infiltrate the porous nickel network. Atthis temperature, the nickel particle layer does not melt or dissolveinto the molten silver, serving as the base structure/design for thelater formation of silver patterns. After solidification, the silvercoverage on the ceramic substrate follows the initial pattern of thenickel paste because the nickel particles remain in place during theheating and cooling process, forming the prescribed pattern. Thisexample illustrates that dense circuit can be produced on ceramicsubstrates. Oxidation has a limited effect on the microstructure becauseAg₂O is not stable above 200° C. The structure was observed to be stableat up to 850° C. in air.

FIG. 6 illustrates an embodiment of the disclosed method in which thesecond metal layer is formed into the desired pattern byself-infiltration into a porous first metal layer having the desiredpattern. The top row images in FIG. 6 illustrate a square latticepattern of porous nickel printed on four different ceramic substrates(alumina, aluminum nitride, yttria-stabilized zirconia, and siliconcarbide, respectively). The second row in FIG. 6 shows a small piece ofsilver foil placed on top of the patterned, porous nickel layer for eachsubstrate. As shown, the silver metal material was not itself patternedand did not have any particular orientation on the porous nickel layer.The third row in FIG. 6 shows that after melting the silver, the moltensilver infiltrated the porous nickel layer, and after solidification,formed a grid pattern just like the initial porous nickel layer. Thesilver was melted by (i) heating at 5° C./min to 1000° C., (ii) holdingat 1000° C. for 2 hr, and (iii) cooling at 5° C./min to ambienttemperature, all performed under an inert argon atmosphere at 20 sccm.The bottom row in FIG. 6 show representative cross-sections after silvermelting and infiltration for the alumina, aluminum nitride, andyttria-stabilized zirconia substrates, where the patterned silver metalforms a continuous metal matrix with elements of the porous nickel layertherein. More generally, if the porous first metal layer pattern isinterconnected and continuous, the second metal can be placed near apart of the porous first metal layer pattern (e.g., on top of, next to)and heated to above the melting point of second metal, which then isdistributed via wetting and spreading throughout the porous first metallayer. Such structures could be useful for current collectors onelectrodes.

The disclosed methods and articles provide several benefits. The methodscan be carried out under inert atmosphere, a condition that is feasiblein many production conditions. The methods and component materials aresuitably non-reactive, for example being free from reactive materialssuch as copper, indium, zirconium, titanium, zinc, tin, manganese,lithium, silicon, and/or species including one or more of theseelements. the methods do not require costly surface depositiontechniques, making them more suitable for industrial applications. Themethods can be combined with 3D printing technologies.

As particularly illustrated in FIGS. 4 and 7, the disclosure relates tomethods of forming a patterned, wetted substrate 100, for exampleincluding a patterned metal layer on a substrate. An initial porouswetting substrate 110 includes an underlying substrate 112 and a porousfirst metal layer 114 on an upper surface 112A of the underlyingsubstrate 112. The first metal layer 114 includes pores 116, for exampleas interstitial pores or other areas between (partially) sinteredparticles of the first metal. The porous first metal layer 114 can bepatterned, for example having been applied in a pattern (e.g., via aprinting technique) or having been patterned after application. Asdescribed below, the porous first metal layer 114 can be formed byapplying a first metal mixture 114A including particles of the firstmetal therein, which particles can then be sintered to form the porousfirst metal layer 114. A (patterned) second metal material 120 is thenapplied to the porous wetting substrate 110, for example atop and incontact with the porous first metal layer 114 thereon. As describedbelow, the second metal material 120 can be applied in the form of a(patterned) layer of a second metal mixture 120A including second metalparticles in a suitable vehicle or liquid formulation. Alternatively,the second metal material 120 can be applied in the form of a metal foilor layer 120B or other solid form of the second metal, in which case thesecond metal material 120 becomes patterned upon eventual heating andmelting of the metal foil 120B. The second metal in the second metalmaterial 120 has a lower melting point than that of the first metal topromote melting, infiltration, and/or spreading of liquid second metalat a temperature that substantially retains the first metal in itsporous form. The second metal material 120 is then heated at atemperature and pressure sufficient to melt the second metal material120, which in turn wets the pores 116 of the porous first metal layer114 with the molten second metal material 122. Likewise, the moltensecond metal material 122 contacts the underlying substrate 112 (e.g.,top surface 112A thereof) to form a wetted substrate 130. The wettedsubstrate 130 includes the underlying substrate 112 and a patterned,wetted second metal layer 124 adhered to the underlying substrate 112(i.e., after cooling and solidification of the molten second metal).

In embodiments, the porous first metal layer has a spatial patterncorresponding to that of the patterned second metal material. The porousfirst metal layer can be formed in the same two-dimensional spatialpattern as the second metal material generally using the same techniquesdescribed below for forming the patterned second metal material, forexample, by printing or otherwise applying a first metal mixtureincluding a first liquid formulation and first metal particles in apredetermined pattern on the substrate, followed by pre-sintering. Insome embodiments, the second metal layer is applied in the desiredpattern on the complementary pattern of the porous first metal layer. Inother embodiments, for example, when the first porous layer has acontinuous and interconnected patterned structure, the second metallayer can be applied over the first porous layer in any desired patternor with no pattern, for example, as a continuous overlayer of secondmetal material. In such cases, upon melting of the second metal, themolten second metal will then be wicked to infiltrate or fill the firstporous metal layer patterned network and become a dense structure withthe same design or pattern of the first porous metal layer (e.g., due tothe relative lack of adhesion between the second metal material andsubstrate). For example, if the lower melting point second metal is incontact (e.g., adjacent or beside) with the first porous metal, thesecond metal could be patterned as adjacent reservoirs and be printed onthe same substrate surface as the higher melting point material, and thesecond metal would be subsequently wicked into the desired pattern ofthe first porous metal layer upon melting. In another embodiment, thelower melting point second metal layer can be deposited on the substrateand below the first porous metal layer (e.g., by methods such assputtering). In such cases, the deposition of the first porous metallayer (e.g., in the desired pattern for the second metal layer) can wetthe sputtered second metal layer and bring the first porous metal layerinto contact with the substrate, thus bonding the second metal layer tothe substrate in the desired pattern. The molten second metal materialnot close to the first porous metal layer will be wicked away from theinterface by the surface tension with the first porous metal layer.

In embodiments, the patterned second metal material has a spatialpattern corresponding to electronic circuitry. For example, thepatterned second metal material can have a spatial pattern that issuitable for electrodes, wires, and/or interconnects. For electroniccircuitry applications, the patterned second metal material suitablyincludes a metal with high electrical conductivity, such as silver orcopper. The minimum dimension (e.g., line width) of the patterned secondmetal material can be controlled, for example, based on the powder sizeof the initial second metal material (e.g., when deposited as asuspension in a liquid formulation prior to melting) and/or thedeposition technique (e.g., screenprinting, 3D printing etc.). Forexample, with the screenprinting used in the illustrative embodiments inthe example, lines with a width as low as about 200 μm can be produced.In other embodiments, minimum pattern line widths of about 50, 80, 100,120, or 150 μm can be used, for example minimum pattern line widths ofat least 50, 80, 100, 120, 150, or 200 μm and/or up to 100, 150, 200,500, or 1000 μm.

The spatial patterns, whether for electronic circuitry or otherwise, canbe formed by lithographic methods, for example where there is a maskthat is preferentially removed to deposit a desired material, such as byelectro deposition. Lithographic methods could be used to providemasking of regions where the first porous metal layer would not beapplied to the substrate, enabling other methods of applying a porousmetal powder onto the exposed substrate, by means of liquid or gasassisted electrostatic methods for particle deposition, on which auniform deposition of the lower melting point second metal materialcould be deposited by various methods, such as sputtering,electrodeposition, etc. Also, additive manufacturing methods could beused to deposit first metal powder particles and concurrently locallyheat the deposited powder to partially sinter particles to adhere to thesubstrate, for example in the desired pattern. More generally, thehigher melting temperature porous first metal layer serves to alter theinterfacial energies between the three components (i.e., first andsecond metals, substrate), thus promoting wetting between the lowermelting temperature second metal layer and the substrate. Any spatialarrangement of the three components can be used, as long as it promotesbonding or adhesion between the lower melting temperature second metaland the substrate (e.g., ceramic or otherwise).

Porous Wetting Substrate Substrates

As particularly illustrated in FIGS. 4 and 7, the disclosure provides aporous wetting substrate 110 including an underlying substrate 112 and aporous first metal layer 114 on a top or upper surface 112A of theunderlying substrate 112.

The underlying substrate of the disclosure is not particularly limited.That is, the method of the disclosure is generally applicable to anysubstrate that is suitable for having a patterned metal layer thereupon.For example, the underlying substrate can include, but is not limitedto, ceramic materials or metal materials.

In embodiments, the underlying substrate includes a ceramic material. Asused herein, a “ceramic material” refers to an inorganic, non-metallicoxide, nitride, or carbide material. The ceramic material can includealuminum oxide, aluminum nitride, gallium nitride, aluminum galliumnitride, aluminum gallium indium nitride, beryllium oxide, zirconiumoxide, cerium oxide, zinc oxide, silicon carbide, silicon nitride,tungsten carbide, lithium oxide, lithium carbide, lithium nitride, oneor more iron oxides, lanthanum strontium manganite, lanthanum strontiumcobaltite, or lanthanum strontium ferrite, doped derivatives thereof, orcombinations thereof. A doped derivative can include any of theforegoing ceramic materials, for example, with up to about 5, 10, or 15wt % of other elements or oxides added thereto.

In embodiments, the ceramic material includes one or more of aluminumoxide (alumina), aluminum nitride, gallium nitride, aluminum galliumnitride, aluminum gallium indium nitride, beryllium oxide, siliconcarbide, or silicon nitride. Alumina, aluminum nitride, beryllium oxide,and silicon nitride, for example, are particularly suitable for circuitboard materials, given their favorable thermal conductivity and abilityto withstand and dissipate heat. Alumina with varying levels of puritycan be used, as well as alumina with different dopants, such aszirconium. Alumina is a suitable substrate for near-room-temperatureelectronics. Ceramics, such as gallium nitride, aluminum gallium indiumnitride, and silicon carbide are particularly suitable for electronicsoperating at high temperature, such as 250° C. to 900° C.

In embodiments, the ceramic metal includes stabilized zirconium oxide,i.e., zirconia. As used herein, the terms “stabilized zirconium oxide”and “stabilized zirconia” are used interchangeably, and refer to aceramic material in which the crystal structure of zirconium dioxide ismade stabilized at room temperature by an addition of an additionaloxide material, such as up to about 10 mol. % of the additional oxidematerial. The stabilized zirconia can include, for example, yttriumoxide (yttria)-stabilized zirconia (YSZ), calcium oxide(calcia)-stabilized zirconia, magnesium oxide (magnesia)-stabilizezirconia, cerium oxide (ceria)-stabilized zirconia, scandium oxide(scandia)-stabilized zirconia (ScSZ), aluminum oxide(alumina)-stabilized zirconia, cerium oxide, doped cerium oxide, orcombinations thereof. Common SOFC solid electrolytes include YSZ such aswith 8 mol % yttria, ScSZ such as with 9 mol % Scandia, and gadoliniumdoped ceria (GDC).

In embodiments, the ceramic material includes one or more of lanthanumstrontium manganite, lanthanum strontium cobaltite, or lanthanumstrontium ferrite. These materials can be useful in SOFC electrodes.

In embodiments, the underlying substrate includes one or more of a metalmaterial or a semiconductor material. Suitable metal and/orsemiconductor materials can include, for example, stainless steel alloyand nickel-based high-temperature alloy. A metallic substrate can beuseful if the second metal, such as silver, does not have very goodwetting properties on the metal substrate. In embodiments, a metallicsubstrate can include a ceramic coating on a surface thereof, such as astainless steel substrate with an alumina coating. The first and secondmetals according to the disclosure can be applied to the ceramic coatingof the substrate.

Porous First Metal Layer

The porous first metal layer is not particularly limited. For example,the porous first metal layer can include a first metal, wherein thefirst metal includes at least one of nickel, aluminum, cobalt, iron,copper, titanium, or combinations thereof. Furthermore, the porous firstmetal layer can include mixtures and alloys of nickel, aluminum, cobalt,iron, copper, and/or titanium.

Some metals such as aluminum, nickel, cobalt, copper could be useful aseither the first or second metal (as described in more detail, below)based on its particular melting point relative to the other metal.Examples of specific combinations of first/second metals include Ni/Ag,Fe/Ag, Co/Ag, Al/Sn, Cu/Bi, and Fe/Bi. The first metal or alloy ispreferably selected for its relative slowness to oxidize, such as Ni,Co, Fe, and Co—Ni (alloy), which have some degree of oxidationresistance and a high relative melting point compared to a second metalselection. In some cases, the first/second metal combinations areselected such that the first and second metals are relatively immisciblein each other such that a bulk layer in the final structure issubstantially composed of a bulk second metal layer (e.g., as an outer,top, or external layer) with only minor amounts of the first metal(e.g., up to 1, 2, 5 wt. % of a minor immiscible component in a primarycomponent). A large portion of the first metal can remain as aninterfacial layer on the underlying substrate, or positioned between thesubstrate and the bulk second metal layer. The interfacial layer caninclude portions of the porous first metal layer remaining at leastpartially or substantially intact as a discrete structure of theinterfacial layer in which the pores have been wetted or infiltrated bythe second metal material. In yet other cases the first metal could bemiscible with the second metal and dissolve into the bulk second metallayer as a homogeneous component (e.g., up to 1, 2, 5, 10, 20, or 30 wt.% of a minor miscible component in a primary component). Preferably, thefirst metal, the second metal, and the substrate are selected based on arelative inability of the second metal to wet the substrate material inisolation, for example being characterized by wetting/contact angles ofthe second metal on the first metal or the substrate materialindividually of at least 20°, 30°, 40°, or 50° when measured in air oran inert atmosphere such as nitrogen. The porous nature of the firstmetal layer promotes efficient wetting by the molten second metal ofboth the porous first metal layer and the first substrate.

The porous first metal layer can have a thickness ranging from about 10nm (0.1 μm) to about 250 μm, about 2 μm to about 250 μm, about 5 μm toabout 100 μm, about 5 μm to about 40 μm, about 10 μm to about 75 μm,about 10 μm to about 30 μm, or about 25 μm to about 50 μm, for example,about 10 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 μm, 2 μm, 3 μm, 5 μm, 8μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 60 μm, 75 μm, 100 μm, 125 μm, 150μm, 175 μm, 200 μm, or 250 μm. The porous first metal layer need nothave a uniform thickness, and the foregoing thickness values canrepresent an average thickness of the porous first metal layer and/or arange for a spatially variable local layer thickness.

The porous first metal layer can include pores ranging in size fromabout 5 nm (0.005 μm) to about 50 μm, about 10 nm to about 50 μm, about1 μm to about 50 μm, about 5 μm to about 30 μm, or about 10 to about 20μm, for example about 5 nm, 10 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 μm,2 μm, 3 μm, 4 μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm,40 μm, 45 μm, or 50 μm. The foregoing pore size values can represent anaverage pore size and/or a range for distributed pore sizes throughoutthe porous first metal layer.

The porous first metal layer can be suitably adhered to the underlyingsubstrate, for example by a pre-sintering process or otherwise. Thedisclosure provides methods of providing the porous wetting substrateincluding applying to the underlying substrate a layer of a first metalmixture including a first liquid formulation and first metal particlesdispersed in the first liquid formulation, and pre-sintering the layerof the first metal mixture at a temperature and pressure sufficient toremove the first liquid formulation and at least partially sinter thefirst metal particles, thereby forming the porous first metal layer.

As provided herein, the first metal mixture can include a first liquidformulation and first metal particles. The first metal mixture issuitably in the form of a solution, thick paste, or suspension thatcoats the first substrate in the target area of interest. The firstmetal mixture can include at least about 30, 50, or 70 wt %, and/or upto 50, 70, or 90 wt % of the first metal particles. Similarly, the firstmetal mixture can include at least about 10, 30, or 50 wt %, and/or upto 30, 50, or 70 wt % of the liquid formulation.

The first metal particles can be of any suitable metal, as provided forthe first metal layer, above.

The liquid formulation can include a liquid solvent medium, such aswater, isopropanol, or any other alcohol or organic solvent. The liquidformulation can also include a liquid binder to improve green strength,such as a polymeric binder dissolved in the aforementioned solventmedium. The liquid formulation can also include a dispersant, such as apolymeric dispersant dissolved in the aforementioned solvent medium, toprevent agglomeration of the first metal particles in a stable firstmetal mixture. In embodiments, the first liquid formulation can includea polymeric solution. The liquid formulation can generally include anypolymer binder, dispersant, resin, or other liquid vehicle. In somecases, the polymeric binder can be a curable binder such that thecorresponding cured binder or resin is degradable at an intermediatetemperature between its curing temperature and the pre-sinteringtemperature. Examples of suitable binder systems include, but are notlimited to, ethylene glycol monobutyl ether, ethylene glycol, andisopropanol.

Pre-sintering generally includes subjecting the first metal mixturelayer to a gradually ramping temperature that removes the liquidformulation, for example degrading, decomposing, etc. any polymeradditives therein and at least partially fusing the first metalparticles to form the porous first metal layer. Sintering generallyincludes applying heat and/or pressure at a level and time sufficient tofuse the particles of the sintering composition without substantialmelting such as to liquefaction. In some alternative embodiments, theporous first metal layer can be applied not only through depositiontechniques, but also by other chemical approaches, for example bycoating the substrate surface with a metal oxide layer, such as NiO,which is then reduced to a corresponding metal, such as Ni, and alsogenerates nano- or meso-scale porosity in the metal during the reductionprocess. In some alternative embodiments, a separate pre-sintering step(a2) before heating the second metal can be omitted, for example whenthe heating of the second metal is sufficient to induce sintering of thefirst metal mixture layer and form the porous first metal layer prior toand/or concurrently with the molten second metal.

When applied to the underlying substrate layer, the first metal mixturecan have a thickness ranging from about 10 nm (0.01 μm) to about 100 μm,about 1 μm to about 100 μm, about 2 μm to about 100 μm, about 5 μm toabout 90 μm, about 5 μm to about 40 μm, about 10 μm to about 75 μm,about 10 μm to about 30 μm, or about 25 μm to about 50 μm, for example,about 10 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 μm, 2 μm, 3 μm, 5 μm, 8μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 60 μm, 75 μm, or 100 μm. Thefirst metal mixture need not have a uniform thickness, and the foregoingthickness values can represent an average thickness of the first metalmixture and/or a range for a spatially variable local thickness.

The first metal particles can have a size ranging from 10 nm (0.01 μm)to about 50 μm, about 1 μm to about 50 μm, about 2 μm to about 50 μm,about 3 μm to about 20 μm, about 5 μm to about 40 μm, about 5 μm toabout 10 μm, about 10 μm to about 30 μm, or about 20 μm to about 25 μm,for example, about 10 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 μm, 2 μm, 3μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, or 50 μm. The size ofthe particles can be determined via a number-, mass-, or volume-averageparticle size or diameter. The first metal particles need not have auniform size, and the foregoing size values can represent an averagesize of the first metal particles and/or a range for spatially variablefirst metal particles. For example, the foregoing size ranges for thefirst metal particles can represent a D10 to D90 span in the cumulativesize distribution function.

In embodiments, the porous first metal layer has a thickness rangingfrom 1 to 10 times, 1.5 to 5 times, 2 to 5 times, 2 to 8 times, 3 to 7times, 4 to 5 times, or 5 to 8 times the average particle size of thefirst metal particles prior to the pre-sintering step. This thicknesscan be determined relative to the number-, mass-, or volume-averageparticle size or diameter of the first metal particles as added to thefirst metal mixture.

In embodiments, the pre-sintering step can include heating the layer ofthe first metal mixture to a maximum temperature ranging from about 600°C. to about 1400° C., about 750° C. to about 1250° C., about 800° C. toabout 1100° C., or about 900° C. to about 1000° C., for example, about600° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C.,1100° C., 1200° C., 1300° C., or 1400° C. Alternatively or additionally,pre-sintering heating can include heating to a maximum temperature thatis at least 100, 200, or 300° C., and/or up to 300, 500, or 700° C.lower than the first metal melting point, such as by ramping fromambient room temperature of first metal mixture application at a rate ofabout 2-10, 50, or 100° C./minute up to the maximum temperature,optionally holding at the maximum temperature for up to 0.1-5 hours, andthen reducing the temperature back to ambient/room temperature at a rateof about 2-10, 50, or 100° C./minute. Pre-sintering is performed at atemperature sufficient to eliminate the liquid formulation throughevaporation of the solvent and/or decomposition or elimination of anypolymeric additives, but less than a temperature sufficient to fullysinter the first metal. At such temperatures, partial sintering/fusingof some particles can occur to a degree sufficient to provide a porousfirst metal structure even in the absence of polymeric additives.

In embodiments, the pre-sintering can occur in a protectivepre-sintering atmosphere. The protective pre-sintering atmosphere can beany inert or protective atmosphere that avoids or prevents oxidation ofthe first metal particles during pre-sintering. Suitable protectivepre-sintering atmospheres can include, for example, an atmosphereincluding at least one of argon or nitrogen. The protectivepre-sintering atmosphere can be essentially completely inert gases suchas argon, nitrogen, or a mixture thereof, such as at least 90, 95, 98,99, or 99.9 mol. % inert gases. A reducing gas such as hydrogen can beincluded in the protective atmosphere to protect against oxidation, suchas at least 1 or 2 mol. % and/or up to 5 or 10 mol. % reducing gas. Theprotective atmosphere is generally at a pressure of about 1 atm orslightly higher to limit entry of external air during pre-sintering. Thepartial pressure of oxygen gas (pO₂) in the protective atmosphere isgenerally selected to maintain a metallic surface on the first metalparticles and porous layer, which can vary with the particular type offirst metal, but is suitably about 10⁻⁶ atm or less in many cases.

Patterned Second Metal Material

As particularly illustrated in FIGS. 4 and 7, the methods describedherein further include applying a patterned second metal material 120 tothe porous wetting substrate 110 and in contact with the porous firstmetal layer 114 thereon. In embodiments, applying the patterned secondmetal material 120 includes applying to the porous wetting substrate apatterned layer of a second metal mixture 120A including a second liquidformulation and second metal particles dispersed in the second liquidformulation. In other embodiments, applying the patterned second metalmaterial 120 includes applying a second metal material 120B such as foilor other solid form of the second metal to the porous wetting substrate110 and in contact with the patterned porous first metal layer 114thereon. Subsequent heating and melting of the second metal material120B can cause the second metal to assume the patterned second metalmaterial 120 form as a complement to the underlying porous first metallayer 114 with its corresponding pattern.

The second metal mixture is suitably in the form of a solution, thickpaste, or suspension that coats the porous wetting substrate in thetarget area of interest. The second metal mixture can be applied on theporous wetting substrate, for example, via a printing process, such asthe application of a liquid or semi-liquid second metal mixture with aprint head in fluid communication with a reservoir of the second metalmixture, in a preselected or predetermined, controlled pattern. Othermethods of applying a patterned second metal material can includetape-casting, deposition, mask coating, and 3D printing.

The second metal mixture can include at least 30, 50, or 70 wt % and/orup to 50, 70, or 90 wt % second metal particles. Similarly, the secondmetal mixture can include at least 10, 30, or 50 wt % and/or up to 30,50, or 70 wt % second liquid formulation.

The second metal material is not particularly limited. For example, thesecond metal material can include a second metal, wherein the secondmetal includes at least one of silver, aluminum, tin, bismuth, nickel,copper, gold, cobalt, or combinations thereof. Furthermore, the secondmetal material can include mixtures and alloys of silver, aluminum, tin,bismuth, nickel, copper, gold, and/or cobalt.

As provided herein, the second metal has a lower melting point that thatof the first metal. For example, the second metal melting point is atleast 25° C., 50° C., 100° C., 200° C., or 300° C. lower and/or up to300° C., 500° C., 700° C., or 1000° C. lower than that of the firstmetal. Similarly, the second metal melting point is suitably lower thanthe melting or thermal decomposition points of the underlying substrate.

The second liquid formulation can include a liquid solvent medium suchas water, isopropanol, or other alcohol or organic solvent. The secondliquid formulation can also include a liquid binder to improve greenstrength, such as a polymeric binder dissolved in the aforementionedsolvent medium. The second liquid formulation can also include adispersant such as a polymeric dispersant dissolved in theaforementioned solvent medium, to prevent the agglomeration of thesecond metal particles in a stable second metal mixture.

In embodiments, the second liquid formulation includes a polymericsolution. The second liquid formulation can generally include anypolymeric binder, dispersant, resin, or other liquid vehicle. In somecases, the polymeric binder can be a curable binder such that thecorresponding cured binder or resin is degradable at an intermediatetemperature between its curing temperature and the heating/meltingtemperature of the second metal material. An example binder systemincludes ethylene glycol monobutyl ether, ethylene glycol, andisopropanol.

In embodiments, the second metal mixture layer has a thickness rangingfrom about 10 nm (0.01 μm) to about 500 μm, about 2 μm to about 500 μm,about 2 μm to about 400 μm, about 5 μm to about 250 μm, about 5 μm toabout 40 μm, about 10 μm to about 100 μm, about 10 μm to about 30 μm, orabout 25 μm to about 50 μm, for example, about 10 nm, 100 nm, 250 nm,500 nm, 750 nm, 1 μm, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 30μm, 40 μm, 60 μm, 75 μm, 100 μm, 125 μm, 150 μm, 175 μm, 200 μm, 250 μm,300 μm, 400 μm, or 500 μm. The second metal mixture need not have auniform thickness, and the foregoing thickness values can represent anaverage thickness of the second metal mixture and/or a range for aspatially variable local thickness. The second metal mixture can becomparable, but generally larger in thickness, relative to that of theeventual patterned, wetted second metal layer.

In embodiments, the second metal particles have a size ranging fromabout 10 nm to about 50 μm, about 1 μm to about 50 μm, about 2 μm toabout 50 μm, about 3 μm to about 20 μm, about 5 μm to about 40 μm, about5 μm to about 10 μm, about 10 μm to about 30 μm, or about 20 μm to about25 μm, for example, about 10 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 μm, 2μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, or 50 μm. Thesize of the particles can be determined via a number-, mass-, orvolume-average particle size or diameter. The second metal particlesneed not have a uniform size, and the foregoing size values canrepresent an average size of the second metal particles and/or a rangefor spatially variable second metal particles. For example, theforegoing size ranges for the second metal particles can represent a D10to D90 span in the cumulative size distribution function.

In embodiments, the second metal mixture layer has a thickness rangingfrom 1 to 10 times, 1.5 to 5 times, 2 to 5 times, 2 to 8 times, 3 to 7times, 4 to 5 times, or 5 to 8 times the average particle size of thesecond metal particles prior to heating. This thickness can bedetermined relative to the number-, mass-, or volume-average particlesize or diameter of the second metal particles as added to the secondmetal mixture.

In embodiments, applying the second patterned second material metalincludes (a1) applying to the underlying substrate a patterned layer ofa first metal mixture including a first liquid formulation and firstmetal particles dispersed in the first liquid formulation; (a2)pre-sintering the patterned layer of the first metal mixture at atemperature and pressure sufficient to remove the first liquidformulation and at least partially sinter the first metal particles,thereby forming a patterned porous first metal layer; (b1) applying thesecond metal material to the porous wetting substrate and in contactwith the patterned porous first metal layer thereon; and (c1) heatingthe second metal at a temperature and pressure sufficient to melt thesecond metal material, wet pores of the patterned porous first metallayer with the molten second metal material, and contact the underlyingsubstrate with the molten second metal material, thereby forming awetted substrate including the underlying substrate, and a patterned,wetted second metal layer adhered to the underlying substrate with apattern corresponding to that of the patterned porous first metal layer.

The heating temperature is suitably sufficiently high to melt the secondmetal material, but far enough below the melting point of the firstmetal, such that the porous first metal layer does not melt or otherwisedisintegrate before its porous structure promotes the wetting andcontact of the underlying substrate with the molten second metalmaterial. The final, solid patterned second metal layer forms aftercooling of the wetted substrate, wherein the second metal material isstill in liquid form, for example by returning to ambient temperatureand pressure conditions without elevated heating temperature and/or aninert protective atmosphere.

In embodiments, the heating of the second metal includes heating thesecond metal to a maximum temperature ranging from about 600° C. toabout 1200° C., about 750° C. to about 1100° C., about 800° C. to about1000° C., or about 900° C. to about 950° C., for example, about 600° C.,700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1100°C., or 1200° C. Alternatively or additionally, heating can includeheating to a maximum temperature that is at least 100, 200, or 300° C.lower and/or up to 300, 500, or 700° C. lower than the first metalmelting point, such as by ramping from ambient room temperature of firstmetal mixture application at a rate of about 2-10, 50, or 100° C./minuteup to the maximum temperature, optionally holding at the maximumtemperature for up to 0.1-5 hours, and then reducing the temperatureback to ambient/room temperature at a rate of about 2-10, 50, or 100°C./minute. The heating process is performed at a temperature andpressure sufficient to melt the second metal material. The molten secondmetal material then wets the pores of the porous first metal layer topenetrate the first metal layer pores and contact the underlyingsubstrate with controlled and/or limited, lateral spreading such thatthe molten second metal material retains substantially the sametwo-dimensional spatial pattern of the patterned second metal materialas applied to the porous wetting substrate. The result of the heatingprocess is a wetted substrate including the substrate and a patterned,wetted second metal layer adhered thereto. Heating generally includessubjecting the second metal to a gradually ramping temperature thatremoves the second liquid formulation, when present, by degrading,evaporating, or decomposing any polymer additives or solvents therein,and melting the second metal particles to form the molten second metaland patterned, wetted second metal layer.

In embodiments, the heating of the second metal can occur in aprotective atmosphere. The protective atmosphere can be any inert orprotective atmosphere that avoids or prevents oxidation of the secondmetal particles during heating. Suitable protective atmospheres caninclude, for example, an atmosphere including at least one of argon ornitrogen. The protective pre-sintering atmosphere can be essentiallycompletely inert gases such as argon, nitrogen, or a mixture thereof,such as at least 90, 95, 98, 99, or 99.9 mol. % inert gases. A reducinggas such as hydrogen can be included in the protective atmosphere toprotect against oxidation, such as at least 1 or 2 mol. % and/or up to 5or 10 mol. % reducing gas. The protective atmosphere is generally at apressure of about 1 atm or slightly higher to limit entry of externalair during heating. The partial pressure of oxygen gas (pO₂) in theprotective atmosphere is generally selected to maintain a metallicsurface on the first and second metal particles and porous layer, whichcan vary with the particular type of first metal, but is suitably about10⁻⁶ atm or less in many cases.

In embodiments, the second metal material includes at least about 90 wt% of the second metal, for example at least about 90 wt %, 95 wt %, 98wt %, 99 wt %, or 99.9 wt % of the second metal, with the balance beingother alloy or impurity elements.

In embodiments, the second metal material is free from air-reactivecomponents. For example, the second metal material can be free fromoxygen-reactive components such as reducible or oxidazable species, suchas copper, indium, zirconium, titanium, zinc, tin, manganese, lithium,and/or silicon, and further including species containing the foregoingelements. For example, the second metal material can be free ofcopper-containing species such as CuO.

Patterned, Wetted Substrate

As particularly illustrated in FIGS. 4 and 7, the patterned second metallayer 124 generally can include at least one or two portions: a bulksecond metal layer 126 and, optionally, an interfacial layer 118 betweenthe bulk second metal layer 126 and the substrate 112. Both the bulksecond metal layer 126 and the interfacial layer 118, when present,generally share the same shape or pattern as the patterned second metallayer 124. For example, provided herein are patterned, wetted substrates100 prepared according to the methods described herein. The patterned,wetted substrates 100 include a substrate 112, the bulk patterned secondmetal layer 124 adjacent to the substrate 112, and (optionally) theinterfacial layer 118 between the bulk patterned second metal layer 124and the substrate 112. The bulk second metal layer 124 includes thesecond metal and optionally the first metal. The first metal, whenpresent in the bulk second metal layer 124, is at a lower concentrationthan the second metal. The interfacial layer 118 includes the firstmetal. Each of the substrate(s), metal(s) and/or metal layer(s) in thepatterned, wetted substrate can be prepared and/or selected asdescribed, above.

In embodiments, the patterned, wetted substrate also includes one ormore electronic components 200 mounted to the patterned, wettedsubstrate 110 in electrical connection to an element of the bulkpatterned second metal layer 126, for example where the bulk patternedsecond metal layer 126 has a spatial pattern corresponding to electroniccircuitry. Two or more electronic components can also be interconnectedwith each other via one or more second metal pattern elements.

The bulk patterned second metal layer, that is, the outer, top, orexternal layer, generally includes only minor amounts of the firstmetal. In embodiments, the bulk patterned second metal layer of thepatterned, wetted substrate has a first metal concentration of 20 wt %or less and the interfacial layer has a first metal concentration thatis at least 10 wt % and greater than the first metal concentration ofthe bulk patterned second metal layer. For example, the bulk patternedsecond metal layer can include at least 0.1, 1, or 2 wt % and/or up to1, 2, 5, 10, 15, or 20 wt % of the first metal, where the concentrationcan represent an average concentration across the bulk second metallayer and/or a range spanning/including the local maximum and minimumconcentration across the bulk second layer. Similarly, the interfaciallayer can include, for example, at least 10, 15, 20, 30, 40, 50, 60, 80,90, or 95 wt. % first metal, where the concentration can represent anaverage concentration across the interfacial layer and/or a rangespanning/including the local maximum and minimum concentration acrossthe diffusion layer. Relative high/low concentrations of the first metalin the interfacial layer and the bulk patterned second metal layer canbe based on the average first metal values in the corresponding layers.

A large portion of the first metal can remain as an interfacial layer onthe substrate, positioned between the substrate and the bulk secondmetal layer. The interfacial layer can include portions of the porousfirst metal layer remaining at least partially or substantially intactas a discrete structure of the interfacial layer in which the pores havebeen wetter or infiltrated by the second metal material. As a result ofthe initially patterned first porous metal layer, the interfacial layercan have the same pattern corresponding to that of the bulk patternedsecond metal layer.

In embodiments, the bulk patterned second metal layer has a second metalconcentration ranging from about 70 wt % to about 99 wt %, about 75 wt %to about 95 wt %, or about 80 wt % to about 90 wt %, for example, about70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt %, 98 wt %, or 99 wt%.

In embodiments, the bulk patterned second metal layer is substantiallyfree from discrete first metal particles having a size greater than 1μm. As used herein, “substantially free,” means that the bulk patternedsecond metal layer suitably contains less than about 1 wt %, 0.5 wt %,0.1 wt %, or 0.01 wt % of discrete first metal particles having a sizegreater than 1 μm. For example, the original porous first metal layerformed during fabrication can essentially be completely disintegrated.The first metal present in the bulk second metal layer can be in theform of a continuous mixture or alloy with the second metal and not asdiscrete larger first metal particles such as those originally used toform the porous first metal layer. Alternatively or additionally, firstmetal present in the bulk second metal layer can be present insub-micron sized discrete particles from the porous first metal layerthat were not completely disintegrated during heating, such as less than1000, 500, 200, 100, or 10 nm in size whether on average or for theentire distribution.

Electronic Apparatus and Component

Further provided herein is an electronic apparatus 200 and methods forforming the same. The electronic apparatus 200 includes an electroniccomponent 210 and patterned, wetted substrate 100 in electricalconnection therewith, for example via the patterned, wetted second metallayer 124 thereof. A suitable method of making the apparatus includesperforming a method as provided herein according to any of its variousembodiments to form the patterned, wetted substrate 100, including theunderlying substrate 112, and the patterned, wetted second metal layer124 adhered thereto. The patterned second metal material 124 has aspatial pattern corresponding to electronic circuitry. One or moreelectronic components 210 are then mounted to the patterned, wettedsubstrate 100 in electrical connection to an element of the patterned,wetted second metal layer 124, thereby providing the apparatus 200.

Two or more electrical components can also be interconnected with eachother via one or more second metal pattern elements. The electroniccomponents and/or integrated electronic systems suitable for manufactureand use as a high-temperature PCB are not particularly limited. Suitableexamples include industries that need higher-frequency connections andgood heat resistance that can benefit from ceramic PCBs, for example,automotive components, aerospace components, medical device components,heavy machinery components, monitors for drilling equipment and relatedcomponents, sensors in heat engines of any kind, RF resistors andterminations, and LED chips.

EXAMPLES

The following examples illustrate methods and articles according to thedisclosure, but are not intended to limit the scope of any of the claimsthereto.

Nickel and silver pastes were produced by hand-mixing 99.9% pure, −400mesh (<37 μm) sized nickel powder (Alfa Aesar Inc.) or 99.9% pure, −325mesh (<44 μm) sized silver powder (Alfa Aesar Inc.) with a V-737 organicvehicle (Hereaus, Inc.) in a 2:1 ratio by weight. The pastes wereapplied to substrates according to either route A or B, as generallyillustrated in FIG. 7. For both routes, the nickel paste was firstscreen-printed onto different ceramic substrates with a designed pattern(e.g., a grid pattern, a circuit-like line pattern) and a variablenumber of printing/coating passes to control the thickness of the nickellayer to have a desired value. Two and three printing passes of nickelpaste were used for route A and B, respectively. Samples were dried at120° C. for 10 minutes after each printing pass. Subsequently, for routeA, a similar screen-printing and drying process was repeated with thesilver paste to achieve a desired layer thickness (six passes total) ontop of the nickel paste-printed substrates, with the silver paste layerhaving generally the same pattern as the underlying nickel layer. Forroute B, a piece of 99.95% pure silver (Alfa Aesar Inc.) with a weightof ˜5 mg was placed atop the nickel paste-printed substrates. Finally,the assemblies in both cases were heated and held at a temperature of820° C. for 2 hours to remove the organic vehicle (e.g., solvent and/orpolymer components thereof) as well as to partially sinter the nickelpowders, thereby forming a porous nickel layer on the substrate. Theassemblies were then heated and held at a temperature of 1000° C. for 30minutes to allow the silver to melt and spontaneously infiltrate thepartially-sintered, porous nickel layer. A ramp rate of 5° C./min wasused for both heating and cooling, and the entire process was performedin 20 sccm of flowing Ar to prevent nickel oxidation.

Both routes A and B can be used to have provide a patterned liquidsilver layer in a controlled shape and at a designated location onvarious ceramic substrates, which in turn solidifies upon cooling toprovide a patterned silver layer that wets and is adhered to theunderlying ceramic substrate.

FIG. 5 shows top-view optical images of a silver circuit with acomplicated, circuit-like line pattern or design on an alumina (Al₂O₃)substrate in different manufacturing stages using route A. Thisillustrates circuit-like line patterns that can be incorporated intoelectronic components such as high power and/or high temperaturecircuits and electronics that use ceramic boards. As shown in FIG. 5,panel A, the silver and nickel material were deposited onto the Al₂O₃substrate with a predesigned (decorative) circuit pattern. The typicalline width and height as printed are ˜540 μm and ˜80 μm, respectively.After heating above the melting point of silver, it is shown in FIG. 5,panel B that the nickel powder had partially sintered into a porouslayer and remained adjacent to the ceramic substrate (e.g., as aninterfacial layer between the substrate and top silver layer), whereasthe silver remained within an upper, bulk surface region consistingprimarily of silver and covering the underlying porous nickel coverage.The overall line width and height remained the same as described aboverelative to panel A, with the silver and nickel materials essentiallyretaining their original as-printed patterns. In the cross-sectionalback-scattered electron (BSE) images (bottom row of each panel), someindividual nickel particles can be observed floating at the top. Withoutintending to be bound by theory, it is believed that these are isolatedparticles that were not sintered into the porous nickel layer.

Similar control experiments with only six silver screen-print passes andno nickel passes were also performed. Due to the lack of a porous nickelor other underlying metal and due to the poor wetting characteristics ofsilver on the ceramic substrate, the silver powder melted and balled-upinto individual spheres that did not bond to the Al₂O₃ substrate at allor otherwise maintain its original printed pattern.

FIG. 5, panel C shows the circuit after being heated and held for 5hours at 850° C. in air. Optically, the circuit pattern exhibited littledifference in the silver portion where no delamination was observed andthe line width remained unchanged, except for the contrast change on theappearance. Without intending to be bound by theory, it is thought thatthis was likely due to the surface oxidation of the silver. Thecross-section shows similar width and height of the lines, and that thenickel network has undergone some oxidation. The darker grey contrastshows that oxidized parts of the nickel network (NiO), and the cores ofsome nickel particles are still not oxidized (lighter grey contrast). Itis noted that the total silver footprint (i.e., the total area of directcontract between the silver and its substrate) on the Al₂O₃ substrateappears to have decreased somewhat. However, the majority of the silveris remains in a shape and position similar to that in FIG. 5, panel B,indicating that there remains good electrical conduction through thesilver circuit lines. In general, the circuit remained dense up to 850°C. in air, which demonstrate the suitability of patterned wettedsubstrates according to the disclosure for use in high-temperatureelectronics.

FIG. 6 shows the creation of a silver grid pattern on alumina (Al₂O₃),aluminum nitride (AlN), yttrium oxide (yttria)-stabilized zirconia(YSZ), and silicon carbide (SiC) substrates (using route. When thedesired pattern is interconnected and continuous like currentcollectors, the silver source material can be a bulk piece of the silvermetal placed within or on a portion of an underlying nickel layer havingthe desired (printed) pattern (e.g., a simple square grid asillustrated). Upon initial heating to a nickel-sintering temperature asdescribed above, the underlying nickel layer becomes a porous nickellayer. Upon further heating to a silver-melting temperature as describedabove, the liquid silver only occupies the silver-philic regions withinthe porous nickel and avoids or limits exposure to the silver-phobicregions where bare ceramic material was exposed and to which silver haspoor wetting and adhesion properties. By a comparing the second andthird rows in FIG. 6, it is clear that the molten silver has infiltratedthe porous nickel layer and assumed the corresponding grid pattern. Thepatterned silver shows a close reproduction of the nickel pattern, forexample exhibiting sharp edges. Likewise, grid holes at the center ofthe pattern that were originally directly under the bulk silver foilpieces (second row) are not covered by silver after infiltration (thirdrow), illustrating a complete wicking and evacuation away from the areasnot intended for silver pattern coverage. The bottom row in FIG. 6 showthe cross-sectional BSE images of the silver-nickel on differentsubstrates. The microstructure shows partially sintered nickel network(grey contrast) with fully infiltrated silver (light grey contrast) andis very similar to that in FIG. 5. This method can be used to producedense current collectors on various ceramic electrodes with well-definedgeometries.

Several nickel powders with different particle sizes were investigatedfor wetting and spreading characteristics of silver on YSZ|NiO—YSZsubstrates. For these example, a porous nickel network prepared asdescribed using a nickel paste that was sintering at about 800° C. for 2hours. As generally described above according to route B, a piece ofsilver was then placed on top of the porous nickel network and melted atabout 1000° C. An observation of top-down infiltration indicates thatthe molten silver infiltrated the portion of the porous nickel directlyunderneath the silver piece. An observation of spreading within thenickel network indicates the molten silver infiltrated and spread acrossthe entire porous nickel network. For nickel powders of −400 mesh (<37μm pass) size and −325 mesh (<44 μm pass) size, both top-downinfiltration and spreading within the porous nickel network wereobserved, suggesting that the porous nickel network was sufficientlystrong (e.g., as characterized by bonding strength between sinterednickel particles, and the mass of the nickel particles) to withstandsurface tension and other straining forces, for example at theinfiltration front of the molten silver, to allow infiltration andspreading throughout the nickel network. For smaller nickel powdershaving a an average size in a range of 3-7 μm, top-down infiltration wasobserved, but not spreading within the porous nickel network. In suchcases, the molten silver broke the nickel network by pulling in nickelparticles and then balling-up. Contrary to the previous example withlarger nickel particle sizes, this suggested that the smaller nickelparticles created a relatively weak porous nickel network. Nonetheless,observation of top-down infiltration indicates that the smaller nickelparticles could be suitable in cases where a corresponding patternedsilver layer is applied atop the underlying patterned nickel layer, inwhich case top-down infiltration is the primary means for wetting andpore-filling (i.e., in contrast to placing an unpatterned silver foil orother bulk solid which requires spreading throughout the porousnetwork).

Accordingly, the examples demonstrate that the methods according to thedisclosure provide control of wetting and spreading of liquid silver onvarious ceramic substrates. It was demonstrated that dense silver layerswere obtained in different shapes and/or designs on alumina, aluminumnitride and yttria-stablized-zirconia substrates.

Because other modifications and changes varied to fit particularoperating requirements and environments will be apparent to thoseskilled in the art, the disclosure is not considered limited to theexample chosen for purposes of illustration, and covers all changes andmodifications which do not constitute departures from the true spiritand scope of this disclosure.

Accordingly, the foregoing description is given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications within the scope of the disclosure may beapparent to those having ordinary skill in the art.

All patents, patent applications, government publications, governmentregulations, and literature references cited in this specification arehereby incorporated herein by reference in their entirety. In case ofconflict, the present description, including definitions, will control.

Throughout the specification, where the compounds, compositions,articles, methods, and processes are described as including components,steps, or materials, it is contemplated that the compositions,processes, or apparatus can also comprise, consist essentially of, orconsist of, any combination of the recited components or materials,unless described otherwise. Component concentrations can be expressed interms of weight concentrations, unless specifically indicated otherwise.Combinations of components are contemplated to include homogeneousand/or heterogeneous mixtures, as would be understood by a person ofordinary skill in the art in view of the foregoing disclosure, andfollowing examples.

PARTS LIST

-   100 patterned, wetted substrate-   110 porous wetting substrate-   112 (underlying) substrate-   112A top or wetted substrate surface-   114 (patterned) porous first metal layer-   114A first metal mixture/layer-   116 pores of first metal layer-   118 interfacial layer-   120 (patterned) second metal material-   120A second metal material in paste or liquid formulation-   120B second metal material in metal foil or other solid form-   122 molten second metal material-   124 patterned, wetted second metal layer-   126 bulk (patterned) second metal layer-   130 wetted substrate-   200 electronic apparatus-   210 electronic component

What is claimed is:
 1. A method for forming a patterned metal layer on asubstrate, the method comprising: (a) providing a porous wettingsubstrate comprising: (i) an underlying substrate, and (ii) a porousfirst metal layer on a surface of the underlying substrate; (b) applyinga patterned second metal material to the porous wetting substrate and incontact with the porous first metal layer thereon, the second metalhaving a lower melting point than that of the first metal; and (c)heating the second metal at a temperature and pressure sufficient tomelt the second metal material, wet pores of the porous first metallayer with the molten second metal material, and contact the underlyingsubstrate with the molten second metal material, thereby forming awetted substrate comprising the underlying substrate, and a patterned,wetted second metal layer adhered to the underlying substrate.
 2. Themethod of claim 1, wherein the porous first metal layer has a spatialpattern corresponding to that of the patterned second metal material. 3.The method of claim 1, wherein the patterned second metal material has aspatial pattern corresponding to electronic circuitry.
 4. The method ofclaim 1, wherein: the first metal comprises at least one of nickel,aluminum, cobalt, iron, copper, titanium and combinations thereof; andthe second metal comprises at least one of silver, aluminum, tin,bismuth, nickel, copper, gold, cobalt, and combinations thereof.
 5. Themethod of claim 1, wherein: the underlying substrate comprises a ceramicmaterial.
 6. The method of claim 5, wherein the ceramic material isselected from the group consisting of aluminum oxide, aluminum nitride,gallium nitride, aluminum gallium nitride, beryllium oxide, zirconiumoxide, cerium oxide, zinc oxide, silicon carbide, silicon nitride,tungsten carbide, doped derivatives thereof, and combinations thereof.7. The method of claim 5, wherein the ceramic material comprises one ormore of aluminum oxide (alumina), aluminum nitride, gallium nitride,aluminum gallium nitride, aluminum gallium indium nitride, berylliumoxide, silicon carbide and silicon nitride.
 8. The method of claim 5,wherein the ceramic material comprises a stabilized zirconium oxide(zirconia).
 9. The method of claim 5, wherein the ceramic materialcomprises one or more of lanthanum strontrium manganite, lanthanumstrontium cobaltite, and lanthanum strontium ferrite.
 10. The method ofclaim 1, wherein the underlying substrate comprises one or more of ametal material and a semiconductor material.
 11. The method of claim 1,wherein the porous first metal layer has a thickness ranging from 0.01μm to 250 μm.
 12. The method of claim 1, wherein the porous first metallayer comprises pores ranging in size from 0.005 μm to 50 μm.
 13. Themethod of claim 1, wherein providing the porous wetting substratecomprises: (a1) applying to the underlying substrate a layer of a firstmetal mixture comprising a first liquid formulation and first metalparticles dispersed in the first liquid formulation; and (a2)pre-sintering the layer of the first metal mixture at a temperature andpressure sufficient to remove the first liquid formulation and at leastpartially sinter the first metal particles, thereby forming the porousfirst metal layer.
 14. The method of claim 13, wherein the first liquidformulation comprises a polymeric solution.
 15. The method of claim 13,wherein the first metal mixture layer has a thickness ranging from 0.01μm to 100 μm.
 16. The method of claim 13, wherein the first metalparticles have a size ranging from 0.01 μm to 50 μm.
 17. The method ofclaim 16, wherein the porous first metal layer has a thickness rangingfrom 1 to 10 times the average particle size of the first metalparticles prior to pre-sintering.
 18. The method of claim 13, whereinpre-sintering comprises heating the layer of the first metal mixture toa maximum temperature ranging from 600° C. to 1400° C.
 19. The method ofclaim 13, comprising performing pre-sintering in a protectivepre-sintering atmosphere comprising at least one of argon and nitrogen.20. The method of claim 1, wherein applying a patterned second metalmaterial comprises: (b1) applying to the porous wetting substrate apatterned layer of a second metal mixture comprising a second liquidformulation and second metal particles dispersed in the second liquidformulation.
 21. The method of claim 20, wherein the second liquidformulation comprises a polymeric solution.
 22. The method of claim 20,wherein the second metal mixture layer has a thickness ranging from 0.01μm to 500 μm.
 23. The method of claim 20, wherein the second metalparticles have a size ranging from 0.01 μm to 50 μm.
 24. The method ofclaim 23, wherein the second metal mixture layer has a thickness rangingfrom 1 to 10 times the average particle size of the second metalparticles prior to heating.
 25. The method of claim 1, wherein applyinga patterned second metal material comprises: (a1) applying to theunderlying substrate a patterned layer of a first metal mixturecomprising a first liquid formulation and first metal particlesdispersed in the first liquid formulation; (a2) pre-sintering thepatterned layer of the first metal mixture at a temperature and pressuresufficient to remove the first liquid formulation and at least partiallysinter the first metal particles, thereby forming a patterned porousfirst metal layer; (b1) applying the second metal material to the porouswetting substrate and in contact with the patterned porous first metallayer thereon; and (c1) heating the second metal at a temperature andpressure sufficient to melt the second metal material, wet pores of thepatterned porous first metal layer with the molten second metalmaterial, and contact the underlying substrate with the molten secondmetal material, thereby forming a wetted substrate comprising theunderlying substrate, and a patterned, wetted second metal layer adheredto the underlying substrate with a pattern corresponding to that of thepatterned porous first metal layer.
 26. The method of claim 1, whereinheating the second metal comprises: (c1) heating the second metal to amaximum temperature ranging from 600° C. to 1200° C.
 27. The method ofclaim 1, comprising performing heating the second metal in a protectiveatmosphere comprising at least one of argon and nitrogen.
 28. The methodof claim 1, wherein the second metal material comprises at least 90 wt.% of the second metal.
 29. The method of claim 1, wherein the secondmetal material is free from air-reactive components.
 30. A method forforming an electronic apparatus, the method comprising: (a) performingthe method of claim 1 to form the wetted substrate comprising theunderlying substrate, and a patterned, wetted second metal layer adheredto the underlying substrate, wherein the patterned second metal materialhas a spatial pattern corresponding to electronic circuitry; and (b)mounting one or more electronic components to the wetted substrate inelectrical connection to an element of the patterned, wetted secondmetal layer.
 31. A patterned, wetted substrate: (a) a substrate; (b) abulk patterned second metal layer adjacent to the substrate, the bulksecond metal layer comprising a second metal and optionally a firstmetal, the first metal being at a lower concentration than the secondmetal in the bulk patterned second metal layer when present; and (c) aninterfacial layer between the bulk patterned second metal layer and thesubstrate, the interfacial layer comprising the first metal; wherein thesecond metal has a lower melting point than that of the first metal. 32.The patterned, wetted substrate of claim 31, further comprising one ormore electronic components mounted to the to the pattern, wettedsubstrate in electrical connection to an element of the bulk patternedsecond metal layer; wherein the bulk patterned second metal layer has aspatial pattern corresponding to electronic circuitry.
 33. Thepatterned, wetted substrate of claim 31, wherein the bulk patternedsecond metal layer has a first metal concentration of 20 wt. % or less;and the interfacial layer has a first metal concentration of at least 10wt. % and greater than the first metal concentration of the bulkpatterned second metal layer.
 34. The patterned, wetted substrate ofclaim 31, wherein the bulk patterned second metal layer has a secondmetal concentration ranging from 70 wt. % to 99 wt. %.
 35. Thepatterned, wetted substrate of claim 31, wherein the bulk patternedsecond metal layer is substantially free from discrete first metalparticles having a size greater than 1 μm.